Method of producing water-soluble nonturbid copolymers of at least one water-soluble N-vinyllactam and at least one hydrophobic comonomer

ABSTRACT

Method of producing vinyllactam copolymers by free-radical polymerization of at least one water-soluble N-vinyllactam and at least one hydrophobic comonomer in an organic solvent in the presence of an initiator under reflux conditions, where the initiator is introduced into the polymerization mixture from below.

BACKGROUND OF THE INVENTION

The present invention relates to a method of producing water-solublecopolymers of at least one water-soluble N-vinyllactam and at least onehydrophobic comonomer by free-radical polymerization of the monomers inan organic solvent, and to the copolymers obtainable by the method andtheir use.

The production of copolymers from N-vinyllactams and hydrophobiccomonomers by free-radical polymerization is known. The production ofsuch copolymers takes place in an organic solvent, for example analcohol or in a mixture of water and organic solvent with a high contentof solvent. Usually, the polymerization is carried out under reflux ofthe solvent. The hydrophobic monomers that are more readily volatilecompared to the N-vinyllactams pass in this way into the gas phase andinto the condensate.

For many application purposes, copolymers are desired which dissolve inwater to give clear solutions, i.e. the FNU value of a 5% strength byweight solution should be <20. However, there is the problem thatdiffering reactivities and differing polarity of the monomers can leadto increases in the concentration of the hydrophobic monomers whichresults in homopolymers which are not water-soluble being able to beformed from the hydrophobic monomers. Even in small amounts in the rangefrom 500 to 1000 ppm, such homopolymers lead to turbidity of an aqueoussolution of the copolymers. The increases in concentration ofhydrophobic monomers can arise in particular in the gas phase and in thecondensate, and also on the reactor wall and the surface of thepolymerization medium.

U.S. Pat. No. 5,395,904 describes the polymerization of vinylpyrrolidoneand vinylacetate by controlled polymerization according to the feedmethod. An alcoholic solvent is used which can comprise up to 50% byweight of water.

U.S. Pat. No. 5,319,041 describes the preparation of copolymers ofvinylpyrrolidone and vinyl acetate by polymerization according to thefeed method with control of the polymerization temperature.

U.S. Pat. No. 5,502,136 describes a method of producing copolymers ofvinylpyrrolidone and vinyl acetate according to the feed method, wherethe feeds are controlled via a scheme defined by specific mathematicalformulae.

U.S. Pat. Nos. 4,520,179 and 4,554,311 describe the polymerization ofvinylpyrrolidone and vinyl acetate with t-butyl peroxypivalate asinitiator in water or water/alcohol mixtures. The initiator used thereinallows the production of copolymers with a narrow molecular weightdistribution, that does not lead to water-soluble products with a FNUvalue of <20.

EP-A 161 describes a method of producing copolymers of vinylpyrrolidoneand vinyl acetate where, after the polymerization, an afterpolymerization with specific initiators is carried out. However, thepolymers have high residual contents of vinyl acetate and are notsufficiently nonturbid.

EP-A 795 567 describes the production of copolymers of vinyllactams andhydrophobic monomers by polymerization in aqueous solution.

EP-A discloses the production of copolymers of vinylpyrrolidone andvinyl esters which dissolve in water to give clear solutions, where, ata certain point during the polymerization, a solvent exchange is carriedout in order to remove volatile constituents. This method is relativelycomplex.

DE-A 22 18 935 describes the copolymerization of N-vinylpyrrolidone withvarious water-soluble and water-insoluble comonomers. Use is made hereof water-insoluble initiators which are used in the form of a finelydivided suspension in an aqueous solution of the copolymers. However, inthe case of the water-insoluble comonomers, this does not likewise leadto the desired water-soluble copolymers with a FNU value of <20.

BRIEF SUMMARY OF THE INVENTION

The object of the present invention is therefore to provide an improvedmethod of producing clearly water-soluble copolymers of at least onehydrophilic N-vinyllactam and at least one hydrophobic comonomer byfree-radical copolymerization in an organic solvent.

According to the invention, the object is achieved by free-radicalpolymerization of at least one water-soluble N-vinyllactam and at leastone hydrophobic comonomer in an organic solvent in the presence of aninitiator under reflux conditions, wherein the initiator, in the form ofa solution in an organic solvent, is introduced into the polymerizationmixture from below.

DETAILED DESCRIPTION OF THE INVENTION

Suitable water-soluble vinyllactams are N-vinylpyrrolidone,3-methyl-N-vinylpyrrolidone, 4-methyl-N-vinylpyrrolidone,5-methyl-N-vinylpyrrolidone, N-vinylpyridone, N-vinylpiperidone,N-vinylcaprolactam, preferably N-vinylpyrrolidone. The vinyllactams areused in amounts of from 30 to 90% by weight, preferably 50 to 90% byweight.

The method according to the invention is suitable for producingwater-soluble polymers of monomer mixtures whose content of hydrophobicmonomers is in the range from 10 to 70% by weight, preferably 10 to 50%by weight, based on the monomer mixture. Suitable hydrophobic monomersare those with a solubility in water in the range from 1 to 100 g/l.Suitable hydrophobic monomers are, for example, vinyl acetate, vinylpropionate, methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butylacrylate, t-butyl acrylate, methyl methacrylate, ethyl methacrylate,acrylonitrile or methacrylonitrile. The hydrophobic monomers are inparticular those whose boiling points at atmospheric pressure are in therange of the polymerization temperature from 60 to 130° C., so that theycan evaporate under polymerization conditions. Even at a boiling pointslightly below the polymerization temperature, the hydrophobic monomercan pass into the gas phase with the solvent if there is adequatemiscibility with the solvent and the solvent boils at polymerizationtemperature. A preferred hydrophobic monomer is vinyl acetate.

Oil-soluble free-radical initiators which may be mentioned are, forexample, dialkyl or diaryl peroxides, such as di-tert-amyl peroxide,dicumyl peroxide, bis(tert-butylperoxyisopropyl)benzene,2,5-bis(tert-butylperoxy)-2,5-dimethylhexane, tert-butyl cumeneperoxide, 2,5-bis(tert-butylperoxy)-2,5-dimethyl-3-hexene,1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane,1,1-bis(tert-butylperoxy)cyclohexane, 2,2-bis(tert-butylperoxy)butane ordi-tert-butyl peroxide, aliphatic and aromatic peroxy esters, such ascumyl peroxyneodecanoate, 2,4,4-trimethylpentyl 2-peroxyneodecanoate,tert-amyl peroxyneodecanoate, tert-butyl peroxyneodecanoate, tert-amylperoxypivalate, tert-butyl peroxypivalate, tert-amylperoxy-2-ethylhexanoate, tert-butyl peroxy-2-ethylhexanoate, tert-butylperoxydiethylacetate, 1,4-bis(tert-butylperoxy)cyclohexane, tert-butylperoxyisobutanoate, tert-butyl peroxy-3,5,5-trimethylhexanoate,tert-butyl peroxyacetate, tert-amyl peroxybenzoate or tert-butylperoxybenzoate, dialkanoyl or dibenzoyl peroxides, such as diisobutanoylperoxide, bis(3,5,5-trimethylhexanoyl) peroxide, dilauroyl peroxide,didecanoyl peroxide, 2,5-bis(2-ethylhexanoylperoxy)-2,5-dimethylhexaneor dibenzoyl peroxide, and peroxycarbonates, such asbis(4-tert-butylcyclohexyl) peroxydicarbonate, bis(2-ethylhexyl)peroxydicarbonate, di-tert-butyl peroxydicarbonate, diacetylperoxydicarbonate, dimyristyl peroxydicarbonate, tert-butylperoxyisopropylcarbonate or tert-butyl peroxy-2-ethylhexylcarbonate.Readily oil-soluble azo initiators used are, for example,2,2′-azobis(isobutyronitrile), 2,2′-azobis(2,4-dimethylvaleronitrile) or4,4′-azobis(4-cyanopentanoic acid).

The oil-soluble free-radical initiator used is preferably a compoundchosen from the group comprising tert-butyl peroxy-2-ethylhexanoate(Trigonox® 21; Trigonox® grades from Akzo Nobel), tert-amylperoxy-2-ethylhexanoate (Trigonox® 121), tert-butyl peroxybenzoate(Trigonox® C), tert-amyl peroxybenzoate, tert-butyl peroxyacetate(Trigonox® F), tert-butyl peroxy-3,5,5-trimethylhexanoate (Trigonox® 42S), tert-butyl peroxyisobutanoate, tert-butyl peroxydiethylacetate(Trigonox® 27), tert-butyl peroxypivalate (Trigonox® 25), tert-butylperoxyisopropylcarbonate, (Trigonox® BPIC),2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (Trigonox® 101),di-tert-butyl peroxide (Trigonox® B), cumyl hydroperoxide (Trigonox® K)and tert-butyl peroxy-2-ethylhexylcarbonate (Trigonox® 117). It is ofcourse also possible to use mixtures of the abovementioned oil-solublefree-radical initiators.

The amount of initiator used, based on the monomers, is in the rangefrom 0.02 to 15 mol %, preferably 0.05 to 3 mol %. In the methodaccording to the invention, the initiator is used as solution, dependingon the solubility, in an organic solvent. Preferably, the same solventas also serves as polymerization medium is chosen. The initiators areparticularly preferably used in a C1-C4-alcohol. In these solutions theinitiator concentration is in the range from 0.02 to 2 mol %, preferably0.1 to 2 mol %, based on the solvent.

A suitable polymerization medium is a polar organic solvent. The solventmust be so hydrophilic that it is miscible with the vinyllactam in anymixing ratio which is achieved during the polymerization. In addition,the solvent should boil under the polymerization conditions so that areflux can form. Of suitability are, for example, aliphatic or aromatichalogenated hydrocarbons, such as chloroform, carbon tetrachloride,hexachloroethane, dichloroethane, tetrachloroethane, chlorobenzene, andliquid C1- or C2-chlorofluorohydrocarbons, aliphatic C2- to C5-nitriles,such as acetonitrile, propionitrile, butyronitrile or valeronitrile,linear or cyclic aliphatic C3- to C7-ketones, such as acetone, methylethyl ketone, methyl isobutyl ketone, 2- or 3-hexanone, 2-, 3-, or4-heptanone, cyclopentanone, cyclohexanone, linear or cyclic aliphaticethers, such as diisopropyl ether, 1,3- or 1,4-dioxane, tetrahydrofuranor ethylene glycol dimethyl ether, carbonates, such as diethylcarbonate, and lactones, such as butyrolactone, valerolactone orcaprolactone. Suitable mono-, di- or polyhydric alcohols are, inparticular, the C1- to C8-alcohols, the C2- to C8-alkanediols, and C3-to C10-tri- or polyols. Examples thereof are methanol, ethanol,n-propanol, isopropanol, n-butanol, sec-butanol, tert-butanol,n-pentanol, 2-pentanol, 3-pentanol, and ethylene glycol, propyleneglycol or 1,3-propanediol.

The monoalkoxy alcohols used are, in particular, the abovementioned C1-to C8-alcohols and C2- to C8-alkanediols, and C3- to C10-triolssubstituted by a C1- to C6-alkoxy group. Examples thereof aremethoxymethanol, 2-methoxyethanol, 2-methoxypropanol, 3-methoxypropanol,2-methoxybutanol, 3-methoxybutanol, 4-methoxybutanol, 2-ethoxyethanol,2-ethoxypropanol, 3-ethoxypropanol, 2-ethoxybutanol, 3-ethoxybutanol,4-ethoxybutanol, 2-isopropoxyethanol, 2-isopropoxypropanol,3-isopropoxypropanol, 2-isopropoxybutanol, 3-isopropoxybutanol,4-isopropoxybutanol, 2-(n-propoxy)ethanol, 2-(n-propoxy)propanol,3-(n-propoxy)propanol, 2-(n-propoxy)butanol, 3-(n-propoxy)butanol,4-(n-propoxy)butanol, 2-(n-butoxy)ethanol, 2-(n-butoxy)propanol,3-(n-butoxy)propanol, 2-(n-butoxy)butanol, 3-(n-butoxy)butanol,4-(n-butoxy)butanol, 2-(sec-butoxy)ethanol, 2-(sec-butoxy)propanol,3-(sec-butoxy)propanol, 2-(sec-butoxy)butanol, 3-(sec-butoxy)butanol,4-(sec-butoxy)butanol, 2-(tert-butoxy)ethanol, 2-(tert-butoxy)propanol,3-(tert-butoxy)propanol, 2-(tert-butoxy)butanol, 3-(tert-butoxy)butanol,4-(tert-butoxy)butanol.

Of particular suitability is a C1- to C4-alcohol, preferably ethanol orisopropanol. Particular preference is given to using isopropanol assolvent.

The polymerization is usually carried out at a neutral pH in the rangefrom 5 to 9. If necessary, the pH is adjusted and/or maintained byadding a base, such as ammonia, triethylamine, triethanolamine, NaOH, oran acid, such as hydrochloric acid, formic acid, acetic acid, lacticacid, oxalic acid, HCl.

If relatively low molecular weights are desired, these can beestablished by adding a regulator to the polymerization mixture.Suitable regulators are, for example, aldehydes, such as formaldehyde,acetaldehyde, propionaldehyde, n-butyraldehyde and isobutyraldehyde,formic acid, ammonium formate, hydroxylammonium sulfate andhydroxylammonium phosphate. In addition, regulators can be used whichcomprise sulfur in organically bonded form. These are, for example,di-n-butyl sulfide, di-n-octyl sulfide, diphenyl sulfide, diisopropyldisulfide, di-n-butyl disulfide, di-n-hexyl disulfide, diacetyldisulfide and di-t-butyl trisulfide. Preferably, the regulators comprisesulfur in the form of SH groups. Examples of such regulators are n-butylmercaptan, n-hexyl mercaptan or n-dodecyl mercaptan. Particularpreference is given to water-soluble, sulfur-containing polymerizationregulators, such as, for example, hydrogen sulfites, disulfites andcompounds such as ethyl thioglycolate, cysteine, 2-mercaptoethanol,1,3-mercaptopropanol, 3-mercaptopropane-1,2-diol, 1,4-mercaptobutanol,mercaptoacetic acid, 3-mercaptopropionic acid, mercaptosuccinic acid,thioglycerol, diethanol sulfide, thiodiglycol, ethylthioethanol,thiourea and dimethyl sulfoxide. Further suitable regulators are allylcompounds, such as allyl alcohol or allyl bromide, benzyl compounds,such as benzyl chloride or alkyl halides, such as chloroform ortetrachloromethane. In a preferred embodiment, the regulator is meteredinto the reaction mixture, if appropriate, as a solution in aC1-C4-alcohol.

In the method according to the invention, the monomers, if appropriateas solution in a C1-C4-alcohol, are metered into the reaction mixture(feed method). In one embodiment of the invention, up to 30% by weight,preferably up to 25% by weight, of the water-soluble N-vinyllactam I(based on the total amount of N-vinyllactam I) and a small amount of theinitiator solution and solvent, preferably ethanol or isopropanol, areinitially introduced. Then, the mixture is brought to the reactiontemperature and the remaining amount of monomer is metered incontinuously or in several portions at the same time as the remainder ofinitiator solution and, if appropriate, a regulator. In general, themetered addition takes place over a period of from 2 to 14 hours,preferably 3 to 12 hours, ideally 4 to 10 hours. Preferably, vinyllactamand hydrophobic comonomer are metered in so that the feeds are completeat the same time. The concentration of the monomers in the reactionmixture is in the range from 10 to 80% by weight, preferably 15 to 70%by weight, based on the reaction mixture. In this case, after thereaction mixture has been brought to the desired reaction temperature,the initiator solution is metered in continuously or in severalportions, in particular over a period of from 2.5 to 16, ideally 4.5 to12 hours.

The polymerization reaction is carried out under reflux conditions. Inthis connection, reflux conditions means that the liquid polymerizationmixture boils and the readily volatile components, such as the solventand/or hydrophobic monomers, evaporate and condense again as a result ofcooling. Reflux conditions are maintained by controlling temperature andpressure.

The reaction temperature can be 60 to 150° C., it is usually in therange from 60 to 90° C. The reaction can be carried out at atmosphericpressure, under autogenous pressure or under protective-gas gagepressure. In the case of protective-gas gage pressure, the pressure isregulated so that boiling is still always present. The person skilled inthe art can determine suitable pressure ranges using the relative vaporpressures. Usually, the pressure here will not exceed 2 MPa. Thepolymerization can take place at a pressure of 0.05 to 2 MPa, preferably0.08 to 1.2 MPa, in particular 0.1 to 0.8 MPa.

The polymerization takes place in a boiler equipped with a stirringdevice. Suitable stirring devices are anchor stirrers, propellerstirrers, cross-blade stirrers, Mik stirrers, and other types ofstirrers suitable for solution polymerizations which are known to theperson skilled in the art. In addition, one or more feed devices formetering the monomers, the initiator solution, and, if appropriate, theregulator (solutions) are also present.

In addition, the boiler, in the upper region of the reactor where noliquid polymerization mixture but a gas phase, is present, is equippedwith a condenser.

Under the polymerization conditions, on account of their lower boilingpoints, solvents and hydrophobic monomers pass in part into the gasphase, whereas the higher-boiling N-vinyllactam remains in the liquidpolymerization phase. In the condenser, the gaseous mixture of solventand hydrophobic monomers condenses and thus forms the so-called reflux.

According to the method of the invention, the initiator solution isintroduced into the polymerization mixture from below by means of asuitable device. in this connection, from below means that the initiatorsolution is introduced below the surface of the liquid polymerizationmixture. Preferably, the introduction takes place in the zone ofgreatest mixing of the liquid polymerization mixture. Where this zone islocated depends firstly on the type of stirrer used, secondly on thereactor geometry. The zone of greatest mixing as a function of the typeof stirrer chosen is known to the person skilled in the art. The personskilled in the art can also ascertain this zone in a simple manner knownper se, usually via computer simulation or color dispersion experiments.

The initiator solution can be introduced into the liquid reactionmixture via customary valves suitable for the introduction of liquids.With the help of metering pumps, the initiator solution can be meteredin continuously or in pregiven metering schemes with variable feed ratesand times.

If there is a plurality of regions of greatest or very great mixing, itis also expedient to introduce the initiator solution as far as possiblebelow the level of the liquid. As a result, the distance between thesite of introduction of the initiator solution and of the reflux ismaximized. Particularly preferably, the introduction takes place abovethe floor of the boiler. The initiator solution can be introduced fromoutside into the reaction mixture, i.e. from the boiler wall, or elsefrom within the boiler chamber by the metering line being run from theboiler wall or the boiler lid inwards and ending within the boilerchamber in a zone which is surrounded at all reaction times by thereaction mixture and is in a zone of greatest possible mixing. In thecase of anchor stirrers, the metering line can thus, for example, runfrom the top into the middle zone of the boiler chamber downwards in thevicinity of the stirrer shaft. In the case of cross-blade stirrers, themetering line can run from the side of the boiler wall into the middlezone between two blades. If the metering line is run into the reactionmixture within the boiler chamber, then this metering line at the sametime acts as flow disrupter and thus increases the desired mixing. Ifappropriate, in the case of such an arrangement, it may also be usefulto incorporate a further flow disrupter as counterpart to the meteringline in order, in so doing, to install two, for example symmetrical,flow disrupters (one or, if appropriate, both of which designed asmetering line) in the boiler. The best arrangement and design as ametering line with or without a further flow disrupter is governed againdepending on the chosen boiler geometry and stirrer type, by the qualityof mixing, which the person skilled in the art can easily ascertain, forexample via computer simulation or color dispersion experiments.

After the polymerization reaction, if desired, one or morepolymerization initiators are additionally added and the polymersolution is heated, e.g. to the polymerization temperature or totemperatures above the polymerization temperature, in order to completethe polymerization. Of suitability are the azo initiators stated above,but also all other customary initiators suitable for a free-radicalpolymerization in alcoholic solution, for example peroxides,hydroperoxides, peroxodisulfates, percarbonates, peroxoesters andhydrogen peroxide. Through this, the polymerization reaction isconducted to a conversion of 99.9%. The solutions which form during thepolymerization usually comprise 10 to 70% by weight, preferably 15 to60% by weight, of polymer. After the polymerization, the solutionsobtained can also be subjected to a physical after treatment, forexample steam distillation or stripping with nitrogen, with the solventor impurities volatile with steam being removed from the solution. Inaddition, a chemical after-treatment or bleaching, for example withhydrogen peroxide or sodium sulfite/tert-butyl hydroperoxide, can alsotake place.

The aqueous solutions of the copolymer obtained by steam distillationcan, if appropriate, be converted into solid powders by a drying processcorresponding to the prior art. Suitable drying processes are thosewhich are suitable for drying from aqueous solution. Preferred processesare, for example, spray-drying, spray fluidized-bed drying, drum-dryingand belt-drying. Freeze-drying and freeze-concentration can likewise beused.

The polymers obtained generally have a K value (determined at 25° C. ina 1% strength by weight aqueous or ethanolic solution) in the range from10 to 100, in particular 10 to 90 and particularly preferably 20 to 80.Determination of the K value is described in H. Fikentscher “Systematikder Cellulosen auf Grund ihrer Viskosität in Lösung” [systematics of thecelluloses based on their viscosity in solution], Cellulose-Chemie 13(1932), 58-64 and 71-74, and Encyclopedia of Chemical Technology, Vol.21, 2nd edition, 427-428 (1970).

A measure of their clear solubility is the nephelometric turbidity unitFNU (or NTU), which is measured at 25° C. in a 5% strength by weightaqueous solution of the polymer and is fixed by calibration withformazin as artificial opacifier. The precise method is given in thecourse of the examples below. The polymers obtained according to theinvention have a FNU value of <20, in particular <10, preferably <7 andparticularly <5.

The polymers obtained by the method according to the invention are usedin particular in cosmetic and pharmaceutical preparations, for exampleas thickeners or film formers in hair lacquer additives, hair settingadditives or hairspray additives, in skin cosmetic preparations,immunochemicals or as active ingredient-releasing agent inpharmaceutical preparations. In addition, the polymers producedaccording to the invention can be used as auxiliaries for agrochemistry,for example for seed coating or for slow-release fertilizerformulations. In addition, the polymers can also be used as coatings forindustrial applications, such as coating of paper or plastics. Thepolymers are also suitable for use in hot-melt adhesives. Furthermore,these polymers are suitable as binders for transfer printing, aslubricant additives, as rust inhibitors or rust removers from metallicsurfaces, as scale inhibitors or scale removers, as auxiliaries duringthe recovery of petroleum from oil-containing water, as auxiliariesduring the production of petroleum and natural gas, and thetransportation of petroleum and natural gas, as cleaners ofwaste-waters, as adhesive raw materials, as detergent additives, and asauxiliaries in the photo industry.

The examples listed below are intended to illustrate the inventionwithout, however, limiting it.

EXAMPLES

General Procedure

The polymerization was carried out in a reactor with a volume of 2 1.The reactor was equipped at the bottom of the reactor with a valve forintroducing the initiator solution (feeds 2 and 4). The initial chargewas flushed with nitrogen for 10 min and heated. As soon as thepolymerization temperature (internal temperature) had reached minus 10%,feeds 1 and 2 were started. Feed 1 was metered in over v h, feed 2 overx h. When feed 1 was complete, feed 3 was metered in over y h. Themixture was then after-polymerized for 1 h. When feed 2 was complete,the mixture was heated to an internal temperature of polymerizationtemperature plus 10%. Feed 4 was then metered in over z h at thistemperature. When feed 4 was complete, the mixture was after-polymerizedfor a further 2 h at this temperature. The majority of the solvent wasthen removed by distillation, and residual amounts were removed by meansof steam distillation. During the steam distillation, water was added asrequired to maintain stirrability. After cooling, water was used, ifappropriate, to establish the particular solids content.

Feed material allocation Amount Unit Initial charge of feed 1 78.4 g offeed 2 3.2 g Feed 1 isopropanol 300 g vinylpyrrolidone 333.2 g vinylacetate 266.7 g Feed 2 isopropanol 50 g tert-butyl perpivalate 75% 2 gFeed 3 vinylpyrrolidone 66.6 g Feed 4 isopropanol 50 g tert-butylperpivalate 75% 2 g tert-butyl perpivalate: 75% in mineral oil(Trigonox ® 25)

Solids content in % by weight

K value measured 1% strength in ethanol

GC analysis: vinylpyrrolidone in ppm; vinyl acetate in ppm;

Appearance: color, clarity, FNU value

FTU value Pol. Example SC K VP VAc 5% in v x y z temp. No. % value ppmppm water [h] [h] [h] [h] ° C. Initiator addition C1 43.2 32.1 14 <10115 11 11 2.5 4 81 above C2 47.9 31.7 32 11 52 11 11 2.5 4 81 above viafeed tube 1) C3 45.3 32.2 23 <10 108 5.5 8 2 3.5 83 above C4 48.9 35.935 <10 36 5.5 8 2 3.5 83 monomers and initiator from below 1 47.6 31.2<10 <10 18 5.5 8 2 3.5 83 below Feed tube which extends below the levelof the liquid from the time when half of the feed materials have beenadded Appearance of the resulting polymerization solutions: Comparisonexample 1: yellowish, turbid Comparison example 2: yellowish, turbidComparison example 3: yellowish, turbid Comparison example 4: yellowish,slightly turbid Example 1: slightly yellowish, clear

1. A method of producing a vinyllactam copolymer, the method comprising:(a) providing at least one water-soluble N-vinyllaetam and at least onehydrophobic comonomer; and (b) free-radical polymerizing the at leastone water-soluble N-vinyllactam and the at least one hydrophobiccomonomer in an organic solvent in the presence of an initiator underreflux conditions, wherein the initiator is introduced into thepolymerization from below, without additional hydrophobic comonomer. 2.The method according to claim 1, wherein the hydrophobic comonomercomprises a monomer having a solubility in water of 1 to 100 g/l.
 3. Themethod according to claim 1, wherein the hydrophobic comonomer comprisesa monomer having a boiling point at atmospheric pressure of 60 to 150°C.
 4. The method according to claim 2, wherein the hydrophobic comonomercomprises a monomer having a boiling point at atmospheric pressure of 60to 150° C.
 5. The method according to claim 1, wherein the hydrophobiccomonomer comprises a monomer selected from the group consisting ofvinyl acetate, vinyl propionate, methyl acrylate, ethyl acrylate,n-propyl acrylate, n-butyl acrylate, t-butyl acrylate, methylmethacrylate, ethyl methacrylate, acrylonitrile, methacrylonitrile, andmixtures thereof.
 6. The method according to claim 4, wherein thehydrophobic comonomer comprises a monomer selected from the groupconsisting of vinyl acetate, vinyl propionate, methyl acrylate, ethylacrylate, n-propyl acrylate, n-butyl acrylate, t-butyl acrylate, methylmethacrylate, ethyl methacrylate, acrylonitrile, methacrylonitrile, andmixtures thereof.
 7. The method according to claim 1, wherein thehydrophobic comonomer comprises vinyl acetate.
 8. The method accordingto claim 4, wherein the hydrophobic comonomer comprises vinyl acetate.9. The method according to claim 1, wherein the N-vinyllactam comprisesN-vinylpyrrolidone.
 10. The method according to claim 8, wherein theN-vinyllactam comprises N-vinylpyrrolidone.
 11. The method according toclaim 1, wherein the polymerization is carried out at a temperature of60 to 150° C.
 12. The method according to claim 10, wherein thepolymerization is carried out at a temperature of 60 to 150° C.
 13. Themethod according to claim 1, wherein the organic solvent comprises analcohol.
 14. The method according to claim 12, wherein the organicsolvent comprises an alcohol.
 15. The method according to claim 1,wherein the initiator is introduced into the polymerization at a zone ofgreatest mixing.
 16. The method according to claim 14, wherein theinitiator is introduced into the polymerization at a zone of greatestmixing.